Method for adjusting a hearing device with frequency transposition and corresponding arrangement

ABSTRACT

A method for adjusting a hearing system to the hearing preferences of a user of said hearing system is disclosed, wherein said hearing system is capable of carrying out frequency transposition of audio signals, which frequency transposition depends on at least one parameter. The method comprises the steps of
     A) carrying out a distinction test for examining said user&#39;s ability to distinguish between two stimulus signals which differ in their frequency contents;   B) adjusting said at least one parameter in dependence of the result of said distinction test.   

     The distinction test comprises the steps
     a2) consecutively playing said two stimulus signals to said user;   b2) receiving from said user information indicative of whether said user perceived said two stimulus signals as two times the same sound or as two different sounds;   c2) deriving a value from said information received from said user;
 
wherein said result of said distinction test is dependent on said value.

TECHNICAL FIELD

The invention relates to an arrangement comprising a hearing system withfrequency transposition and method for adjusting such a hearing system.

Under a hearing device, a device is understood, which is worn in oradjacent to an individual's ear with the object to improve theindividual's acoustical perception. Such improvement may also be barringacoustic signals from being perceived in the sense of hearing protectionfor the individual. If the hearing device is tailored so as to improvethe perception of a hearing impaired individual towards hearingperception of a “standard” individual, then we speak of a hearing-aiddevice. With respect to the application area, a hearing device may beapplied behind the ear, in the ear, completely in the ear canal or maybe implanted.

A hearing system comprises at least one hearing device. In case that ahearing system comprises at least one additional device, all devices ofthe hearing system are operationally connectable within the hearingsystem. Typically, said additional devices such as another hearingdevice, a remote control or a remote microphone, are meant to be worn orcarried by said individual. Analogously, a hearing-aid system comprisesat least one hearing-aid device.

For purposes of this patent application, frequency transposition means aspectral modification of audio signals, which comprises shifting atleast a portion of said audio signals from its original frequency rangeto a different frequency range. Frequency transposition typicallycomprises frequency shifting and/or frequency compression, whereinfrequency shifting means that a portion of audio signals of an originalfrequency range is shifted to a new frequency range of the samefrequency width in octaves, and frequency compression means that aportion of audio signals of an original frequency range is shifted to anew frequency range which has a different frequency width. Frequencytransposition may also comprise reducing the playback speed of recordedaudio signals while discarding portions of the signal in order topreserve the original duration.

Under audio signals we understand electrical signals, analogue and/ordigital, which represent sound.

BACKGROUND OF THE INVENTION

From U.S. Pat. No. 4,637,402, it is known to measure the hearing deficitof a person and to fit a hearing aid to said person. Frequency bands aredetermined over which said person's hearing level is unacceptable, andthese bands are then shifted—in a harmonic-sustaining manner—to bandswith an acceptable hearing level. Said frequency bands are determined bymeans of a swept frequency tone generator. Furthermore, after initialvalues are chosen for the various gains and gainshaping elements, saidperson is then presented with well known word discrimination lists, i.e.spoken words which are known to differ in subtle ways from other words,and his test scores are taken. On the basis of the types of words thatare missed and the spectral content of those words, the appropriate gainchanges, and if necessary transposition placements and characters arealtered. I.e., a recognition test is carried out, and dependent on theresult of that recognition test, parameters related to the frequencytransposition are altered.

In U.S. Pat. No. 6,212,496, a technique for producing an audio outputcustomized to a listener's hearing impairment through a digitaltelephone is disclosed. By determining hearing thresholds for manyfrequencies, unacceptable regions (frequency ranges) are determined, inparticular frequency bands in which the user cannot hear. Theunacceptable band or bands is/are then mapped onto one or moreacceptable bands.

It is desirable to provide an alternative way of adjusting parametersrelated to frequency transposition in a hearing system, and to provide aarrangement for carrying out such adjustments.

In WO 2004/054318 A1, a method for fitting a portable hearing device toa hearing-impaired user is disclosed. The method shall lead towell-adjusted frequency-dependent gain curves and comprises a consonantdiscrimination step, in which an A-B-discrimination test with the soundof the letter “s” present or absent is carried out. If the user can hearthe difference, high frequencies are left unchanged; if the user cannothear the difference, high frequencies are boosted. There is no mentionof frequency transposition.

From EP 1 441 562 A2, hearing devices are known, in which frequencytransposition is implemented. Methods for carrying out frequencytransposition, in particular frequency compression, are thereindisclosed in detail.

In B. C. J. Moore “A test for the diagnosis of dead regions in thecochlea”, British Journal of Audiology Vol. 34, No. 4, 2000, pages205-224, a procedure for measuring psychophysical tuning curves (PTCs)is disclosed. Said procedure comprises, for several test frequencies,determining the threshold of perception of a sinusoid of said testfrequency in presence of a masker, wherein a noise band was used as themasker.

SUMMARY OF THE INVENTION

One object of the invention is to create a method for adjusting ahearing system with frequency transposition that provides an alternativeto known methods. In addition, an arrangement for doing so shall beprovided. And a use of distinction tests is provided, too.

Another object of the invention is to provide for an alternative way todetermine candidacy of a user for the use of frequency transposition inthe user's hearing system.

Another object of the invention is to provide for a method and anarrangement for adjusting a hearing system with frequency transposition,which can be used without or with only little prerequisites.

Another object of the invention is to provide for a way of adjusting ahearing system with frequency transposition, which is particularly fast,i.e., which can be carried out within a relatively short time.

Another object of the invention is to provide for a way of adjusting ahearing system with frequency transposition, which yields particularlyreliable results.

Further objects emerge from the description and embodiments below.

At least one of these objects is at least partially achieved by methodsand arrangements according to the patent claims.

The method for adjusting a hearing system to the hearing preferences ofa user of said hearing system, wherein said hearing system is capable ofcarrying out frequency transposition of audio signals, which frequencytransposition depends on at least one parameter, comprises the steps of

-   A) carrying out a distinction test for examining said user's ability    to distinguish between two stimulus signals which differ in their    frequency contents;-   B) adjusting said at least one parameter in dependence of the result    of said distinction test.

The use according to the invention is a use of a distinction test inwhich the ability of a hearing system user to distinguish between twostimulus signals which differ in their frequency contents isinvestigated, for adjusting at least one parameter of said hearingsystem, which is capable of carrying out frequency transposition ofaudio signals, and wherein said frequency transposition depends on saidat least one parameter.

Through this, an improved and/or simplified adjustment of said hearingsystem can be achieved. And/or it can be determined whether or not theuse of frequency transposition is beneficial for said user.

As has been described above, from U.S. Pat. No. 4,637,402, it is knownto use a recognition test (for certain words) in order to find outsuitable values for parameters related to frequency transposition. Arecognition test always asks the question “Is a certain soundrecognized?” or “Does a certain sound remind of a sound known before?”.Accordingly, a recognition test, such as a speech recognition test or aspeech intelligibility test, relates to previous knowledge.

In U.S. Pat. No. 6,212,496, on the other hand, detection tests arecarried out in order to find out suitable values for parameters relatedto frequency transposition. In a detection test, the question “Can Ihear a certain sound?” is asked. Detection tests are typically used fordetermining threshold values, such as the hearing thresholds in U.S.Pat. No. 6,212,496. Accordingly, in detection tests, a level (thresholdlevel) of a signal is determined at which a signal is barely or just notperceivable.

So far, the use and adjustment of frequency transposition features inhearing devices was basically linked to the detection of “unacceptable(frequency) regions”, i.e. frequency ranges with particularly highhearing thresholds were used as an indicator for the use of frequencytransposition and/or as a magnitude for determining values to beassigned to parameters related to the frequency transposition.

The inventors, however, found that the determination of the hearingsystem user's ability to distinguish between sounds of differentfrequency contents is a good indicator for the use of frequencytransposition, and moreover, from examining said ability, informationcan be gained for adjusting parameters related to the frequencytransposition.

Furthermore, the inventors found that while in many cases the existenceof “unacceptable (frequency) regions” is a decent indicator for the useof frequency transposition, there are also cases in which no pronounced“unacceptable (frequency) region” exists, but nevertheless, frequencytransposition turned out to be beneficial for the hearing system userand, vice versa, that there are cases in which frequency transpositiondid not turn out to be helpful despite the existence of pronounced“unacceptable (frequency) regions”.

And moreover, the inventors found that investigating the hearing systemuser's ability to distinguish between signals in frequency space(instead of determining amplitudes) can be carried out beneficially in adistinction test. A distinction test always asks whether or not adifference can be perceived, such as “Can I hear a difference betweenthe two sounds played to me? (Or are they indistinguishable to me?)” or“Which one of those (three or more) sounds is different from theothers?”.

From the result of such a distinction test, valuable information can beobtained with respect to the question of whether or not the use offrequency transposition will be beneficial for a user and/or whichvalues should be selected in adjusting parameters related to thefrequency transposition.

A distinction test needs only little prerequisites. It is relativelystraight-forward for an individual tested in a distinction test todecide whether or not one perceives stimulus sounds as equal or asdifferent. Unlike in recognition tests, no reference has to be made topreviously known sounds, and there is also no indispensable need forfirstly making a practically full fitting of the hearing system andwaiting through an acclimatization time before starting a recognitiontest.

In a very simple embodiment, two stimulus signals of different frequencycontents could be played to the user, and the user is asked to indicatewhether he perceived the two signals as two times the same signal or astwo different signals. If the user is able to distinguish the twosignals, a default frequency transposition (with default parametersettings) will be invoked, whereas the frequency transposition featureis not used (switched off; neutral parameter adjustments) if the userperceives the difference.

In one embodiment, said hearing system is a hearing-aid system. In thiscase, said hearing preferences of said user will most importantly bedetermined by the user's hearing impairment.

In one embodiment, said frequency transposition is carried out bytransforming audio signals into frequency space, thus obtaining aspectrum, transposing at least a portion of said spectrum to a differentfrequency range (shifting and/or compressing), thus obtaining a modifiedspectrum, and transforming said modified spectrum into time space, thusobtaining modified audio signals.

Examples for said parameter are a cutoff frequency, e.g., defining afrequency above which frequency compression sets in or a frequencylimiting a frequency range to be shifted; a compression ratio; afrequency shift.

In one embodiment, said distinction test is related to a test frequency,and said two stimulus signals are both chosen in dependence of said testfrequency.

In one embodiment, said distinction test is related to a test frequency,and said two stimulus signals are chosen such that the sum of theiraudio frequency spectra is substantially symmetrical with respect tosaid test frequency. The term “symmetrical” is preferably meant in anauditory sense, i.e. rather on a logarithmical Hertz scale than on alinear Hertz scale.

We used that term “audio frequency spectrum” in order to exclude lowfrequencies, in particular frequencies which are not audible. E.g., inthe case of warbling sounds (pitch modulated sounds), the (low)modulation frequency shall not be considered.

In one embodiment, said distinction test relates to a test frequency,and each of said two stimulus signals has an audio frequency spectrum,which is substantially symmetrical with respect to said test frequency.

In one embodiment, said distinction test relates to a test frequency,and the audio frequency spectrum of one of said two stimulus signals issubstantially symmetrical with respect to the audio frequency spectrumof the other of said two stimulus signals, with said test frequencyforming substantially the corresponding symmetry axis.

In one embodiment, said two stimulus signals are substantially noiseshaving different band widths, in particular narrow-band noises, e.g.,having widths of one or two octaves or (rather) less. In particular,said noises with different band widths may have the same main frequency,in particular wherein said main frequency is substantially identicalwith said test frequency.

In one embodiment, said two stimulus signals are substantiallynarrow-band signals of different frequencies, in particular sine signalsor narrow-band noises. Preferably, each of said narrow-band signals hasa main frequency forming substantially the same interval with said testfrequency, one above and one below said test frequency.

In one embodiment, said two stimulus signals are substantiallynarrow-band signals warbling with different warbling amplitudes aroundsubstantially the same middle frequency. Said narrow-band signals canbe, e.g., sine signals or narrow-band signals. In particular, saidmiddle frequency is substantially identical with said test frequency.

In one embodiment, carrying out said distinction test comprises

-   a2) consecutively playing said two stimulus signals to said user;-   b2) receiving from said user information indicative of whether said    user perceived said two stimulus signals as two times the same sound    or as two different sounds;-   c2) deriving a value from said information received from said user;    wherein said result of said distinction test is dependent on said    value.

In one embodiment, carrying out said distinction test comprises

-   a3) consecutively playing three stimulus signals to said user,    wherein these three are chosen from said two stimulus signals either    freely or such that one of said two stimulus signals is played    exactly once;-   b3) receiving from said user information indicative of which of said    consecutively played three stimulus signals was perceived as    different from the other two, or indicative of which of said    consecutively played three stimulus signals was perceived as    different from the other two or whether all three consecutively    played three stimulus signals were perceived as three times the same    sound;-   c3) deriving a value from said information received from said user;    wherein said result of said distinction test is dependent on said    value.

It is possible to choose said three stimulus signals such that one ofsaid two stimulus signals is played exactly once, in which case it canbe advantageous to force the user to identify one of the three playedstimulus signals as different from the other (“forced choice”; theanswer “all three seemed equal” excluded). It is, however possible, toallow the answer “all three seemed equal”.

On the other hand, it is possible to allow for a free choice of saidthree stimulus signals played to the user, in which case playing threetimes the same stimulus signal would be possible, so that thecorresponding answer of the user would be allowed.

In one embodiment, before step A), the step of

-   G) determining a gain model suitable for said user and using said    gain model during step A);    is carried out. A gain model represents the basic amplification    characteristic in dependence of input level and frequency (basic    frequency-dependent amplification function). The determination of    gain models is a well-known procedure in the fitting of hearing    devices.

Carrying out said distinction test using said before-determined gainmodel can lead to more reliable results, in particular if stimulussignals are used, which differ strongly with respect to their mostprominent frequency.

In one embodiment, before step A), the step of

-   L) adjusting said two stimulus signals to substantially the same    loudness;    is carried out. This way, it can be avoided that the user perceives    signals as different, which he otherwise would not be able to    distinguish (with respect to their frequency contents), only because    of there is a loudness difference between them. Step L) can be    accomplished, e.g., by playing said two stimulus signals to the user    and adjusting their output level until the user says that he    perceives the two stimulus signals as having the same level (note    that “loudness” is a subjective magnitude, individual to the    perceiving person). It can be advantageous to adjust said two    stimulus signals to having the same signal power, e.g., the same    signal pressure level (SPL), before carrying out step L).

In one embodiment, the frequency contents of said two stimulus signalsis related to a test frequency, and method comprises the steps of

-   -   carrying out step A) at least twice for the same test frequency;    -   adjusting said at least one parameter in dependence of the        results of said distinction tests.

An improved setting of said parameter can be achieved when it is basedon more reliable data. This can be achieved in the indicated way. Adetailed evaluation, in particular using statistical methods, of theresults of the distinction tests can lead to improved parameter settingsand thus to higher contentness of the user with his hearing system. StepA) can advantageously be carried out at least 3 or 4 times, preferablyat least 5 or 6 times. Usually, carrying out step A) 12 to 15 times willbe advantageous, whereas more than 20 or 25 times tend to strain theuser more than would be justified by the achieved increase inreliability.

In one embodiment, the frequency contents of said two stimulus signalsis related to a test frequency, and said method comprises the steps of

-   -   carrying out step A) at least once for each of at least two        different test frequencies;    -   adjusting said at least one parameter in dependence of the        results of said distinction tests.

Investigating said user's ability to distinguish between two stimulussignals which differ in their frequency contents at two or moredifferent frequencies will usually give a better judgement on the user'scandidacy for the use of frequency transposition, and also the parametersettings obtained this way are expected to suit the user's needs better.Two, better 3, possibly 4 or 5 different frequencies can beinvestigated. It is possible to investigate 6 or more differentfrequencies, but since it can be advantageous to carry out severaldistinction tests for each test frequency, the number of distinctiontests the user is asked to participate in could in that case easilybecome too high for the user.

Preferably, the results of the several distinction tests are evaluated,in particular statistically, and the adjustment of said at least oneparameter depends on the result of said evaluation.

In one embodiment, the method comprises carrying out step A) a multitudeof times, each time comprising the steps of

-   x) choosing at least a first and a second stimulus signals from said    two stimulus signals;-   a) playing the chosen stimulus signals to said user;-   b) receiving from said user information in reaction to step a);-   c) deriving a value from said information received from said user;    wherein said result of said distinction test is dependent on said    value, and wherein said information received from said user is    indicative of whether or not said user perceived one of said chosen    stimulus signals as different from at least one other of said chosen    stimulus signals and/or indicative of which one of said chosen    stimulus signals has been perceived by said user as different from    at least one other of said chosen stimulus signals.

In one embodiment, said value derived in step c) is indicative of theagreement or disagreement, respectively, between said informationreceived from said user and the relation between said chosen stimulussignals.

For example, one value, e.g., 1 (one), could be granted if the user'sperception of the stimulus signals is in agreement with the truerelation between the stimulus signals, and another value, e.g., 0(zero), could be granted if the user's perception of the stimulussignals is different from the true relation between the stimulussignals. In case of a disagreement between the user's perception andtrue relation between the stimulus signals, one could furthermoredifferentiate between a perception of a difference where the stimulussignals were identical (“false positives”) and a perception of nodifference where the stimulus signals were different. These two casescould be assigned different values and/or only one of them could beevaluated or both could be evaluated in a different manner.

Such a value could be termed “agreement value” since it is related tothe kind or type or amount of agreement between the user's perceptionand the true relation between the stimulus signals. Such a value can beconsidered to be indicative of the relation between said informationreceived from said user and the true relation between said chosenstimulus signals.

In one embodiment, the method comprises the step of

-   D) statistically evaluating said values derived in step c) for said    multitude of times of carrying out step A),    wherein said adjusting said at least one parameter is dependent on    the result of said statistical evaluation.

In one embodiment, the method comprises repeating step A) after step B).This can be valuable to verify that the parameter adjustment hasimproved the user's perception.

The arrangement according to the invention comprises

-   -   a signal processing unit comprised in said hearing system, for        carrying out frequency transposition of audio signals, which        frequency transposition depends on at least one parameter;    -   a sound generating unit for generating stimulus signals;    -   a user interface for receiving user input;    -   a control unit operationally connected to said signal processing        unit, said sound generating unit and said user interface, and        adapted to carrying out a distinction test for examining the        ability of a user of said hearing system to distinguish between        two stimulus signals which differ in their frequency contents;        wherein said control unit is furthermore adapted to adjusting        said at least one parameter in dependence of the result of said        distinction test.

Said sound generating unit is preferably comprised in said hearingsystem.

Said sound generating unit may be part of said signal processing unit.

Said user input generally reflects input from the user of the hearingsystem. It may be entered by the user, but possibly is entered by ahearing device professional such as a hearing device fitter or anaudiologist.

In one embodiment, said arrangement is a hearing system. In this case,it would be possible that the user himself would adjust said at leastone parameter, possibly without or largely without external assistance.

The advantages of the arrangements correspond to the advantages ofcorresponding methods.

Further preferred embodiments and advantages emerge from the dependentclaims and the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, the invention is described in more detail by means of examplesand the included drawings. The figures show schematically:

FIG. 1 a block diagram of a method according to the invention;

FIG. 2 a block diagram of a distinction test;

FIG. 3 an illustration of a pair of stimulus signals;

FIG. 4 an illustration of a pair of stimulus signals;

FIG. 5 an illustration of a pair of stimulus signals;

FIG. 6 an illustration of frequency compression;

FIG. 7 an illustration of a method and an arrangement according to theinvention;

FIG. 8 an illustration of an arrangement according to the invention.

The reference symbols used in the figures and their meaning aresummarized in the list of reference symbols. The described embodimentsare meant as examples and shall not confine the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block diagram of a method according to the invention. Instep 100, the procedure for adjusting at least one parameter influencinga frequency transposition in a hearing system starts. In optional step200, stimulus signals to be used later in the procedure are adjusted toequal loudness (with respect to the perception of a user of the hearingsystem). In steps 300 to 400, distinction tests are carried out for mdifferent test frequencies, wherein Ni (i=1, . . . , m) distinctiontests are carried out for the mth test frequency. The distinction testsare described in more detail in FIG. 2.

In step 500, the results of the distinction tests are evaluated, e.g.,using statistical methods. In step 600, finally, said at least oneparameter is adjusted in dependence of the evaluation.

FIG. 2 shows a block diagram of a distinction test. The distinction testis a test for examining said user's ability to distinguish between twostimulus signals which differ in their frequency contents. In step 310,from typically two different stimulus signals, a first and a secondstimulus signals are chosen; it is also possible to choose a thirdstimulus signal and possibly even further stimulus signals from said twodifferent stimulus signals. The choice of the at least two stimulussignals can, e.g., be a random choice.

In step 320, the chosen stimulus signals are consecutively played to thehearing system user. Upon perception of the stimulus signals played tohim, the user will, in step 330, provide a user input. The user inputprovides user information indicative of whether the user perceived theplayed stimulus signals as a repetition of always the same sound or assounds of which at least one is different, and/or the user inputprovides user information indicative of which of said consecutivelyplayed stimulus signals was perceived as different from the others.

In step 340, the user information is evaluated, in particular bycomparing it to the true relation between the played stimulus signals.In step 350, finally, the test results, i.e. the results obtained instep 340, are output.

It is possible to carry out the procedure for each ear separately, orfor both ears simultaneously.

In FIGS. 3, 4 and 5, different examples of pairs of stimulus signals areillustrated, for a test frequency f0. The stimulus signals played to theuser during a distinction test, can be chosen from one of these pairs(cf. step 310 in FIG. 2). The horizontal axis is a preferablylogarithmical frequency axis (f), and the vertical axis is an intensity,e.g., an SPL. The illustrated signals are rather easily to generate andcan preferably be generated in a hearing device of the hearing system.

FIG. 3 illustrates narrow-band noise signals centered around f0 andhaving different widths. Typical widths for the noises are half anoctave to 2 octaves for the wider noise and half an octave to a secondor a third for the narrower noise. Such noise signals can be generated,e.g., by band-pass filtering white or pink or other noise.

FIG. 4 illustrates sine-signals of frequencies f1, f2 close to f0,having substantially the same distance interval with respect to f0. Theintervals f0-f1 and f2-f0 are typically between a second and an octave.

FIG. 5 illustrates warbling sine-signals with center frequency f0,having different warbling amplitudes Δf1 and Δf2, respectively. Thewarbling is illustrated by the dotted lines and may have a frequency ofthe order of 1 Hz. The warbling amplitudes Δf1, Δf2 have typically thesame widths as mentioned above for the widths of the noises in FIG. 3.

Typical test frequencies are in the range 0.8 kHz to 8 kHz, moretypically in the range 1.2 kHz to 6 kHz.

Concrete Example

In this example, the frequency transposition to be optimized for theuser is a non-linear frequency compression (non-linear with respect to alinear Hertz scale, but linear on a logarithmic Hertz scale), e.g., asdefined in the above-mentioned EP 1′441′562 A2. It is configurable bysetting a cutoff frequency fc and a compression rate CR. The compressionrate CR defines the ratio of the frequency width of an interval of aninput audio signal to the frequency width of an interval of an outputaudio signal. E.g., compression rate CR is the ratio of the logarithm ofan input bandwidth in Hertz and the logarithm of an output bandwidth inHertz.

Compression takes place only above the cutoff frequency fc and causes adown-shifting. When measured in Hertz, higher frequencies are shiftedmore than lower ones.

FIG. 6 is an illustration of frequency compression as described above.

For the frequency transposition to be optimized for the hearing systemuser, the cutoff frequency fc is preferably adjustable within apre-defined range, for example with a minimum cutoff frequency offc_min=1.5 kHz and a maximum cutoff frequency of fc_max=3 kHz.Preferably, the test frequencies for which distinction tests areperformed lie within this range. In the present example, the compressionrate CR has a pre-defined value, e.g., in the range of 1.5:1 to 3:1. Itis also possible to choose frequency-dependent compression rates CR. Andit is also possible to derive a value for the compression rate CR fromthe results of the distinction tests.

In the present example, the only parameter to be adjusted in dependenceof the results of the distinction tests is the cutoff frequency fc.

Distinction tests are performed at m=3 different test frequencies f0,namely 1.5 kHz, 2 kHz and 3 kHz.

At each of these test frequencies f0, the test is repeated several times(Nm times), preferably five to fifteen times (Ni=5 . . . 15), forexample twelve times (N1=N2=N3=12).

For each distinction test, two stimulus signals are chosen from twonarrow-band noises centered about the corresponding test frequency f0(cf. FIG. 3) and played to the user one after the other. Accordingly, ifthe two stimulus signals from which the stimulus signals to be playedare chosen are labelled A and B, respectively, (cf. FIG. 3), one of thestimulus signals pairs A-A, A-B, B-A, B-B will be played during eachdistinction test. Upon perceiving a stimulus signals pair, the user willindicate, e.g., by telling his hearing device fitter or by manipulatingan appropriate button of a user interface of the hearing system, whetherhe perceived the stimulus signals pair as two times the same sound or astwo different sounds.

Preferably, the distinction test results are represented as percentagevalues p, varying between 100% for agreement between the user'sperception of the agreement or disagreement between the played stimulussignals and the true agreement or disagreement between the playedstimulus signals (perfect distinction), and 0% if the user perceivedequal stimulus signals as different stimulus signals or differentstimulus signals as equal stimulus signals. The results of differenttest frequencies are preferably averaged to yield an averaged valuep_avg:

p_avg=⅓×(p(1.5 kHz)+p(2 kHz)+p(3 kHz))

The averaged value p_avg will amount to 50% if the user can only guess(no distinction).

The cutoff frequency fc is preferably calculated such that

p_avg=100%→fc=fc_max (i.e. 3 kHz)

p_avg 50%→fc=fc_min (i.e. 1.5 kHz),

i.e. such that if the user's perception is fully correct in alldistinction tests, the highest possible cutoff frequency is chosen, andif the user input is always in disagreement with the true relationbetween the stimulus signals, the lowest possible cutoff frequency ischosen. For intermediate values of p_avg, fc should be interpolatedbetween fc_min and fc_max.

For fc_min=1.5 kHz and fc_max=3 kHz, the cutoff frequency fc cantherefore be obtained as

fc=p_avg×3 kHz.

It is possible to use the described procedure for determining candidacyof a user for the use of frequency transposition. E.g., if p_avg isabove 90%, frequency transposition could be switched off, whereasfrequency transposition would be used with the above-described parameter(fc) if p_avg 90%.

Of course, more elaborate schemes for determining parameter settingsfrom the results of the distinction test can be chosen.

In particular, it is possible to carry out distinction tests in anadaptive fashion. In that case, the two stimulus signals to choose fromcan be chosen in dependence of results of previous distinction tests.E.g., one could start with easily distinguishable stimulus signals,e.g., a 1.5 octaves wide noise signal and a noise signal of a secondonly (cf. FIG. 3), and if in one or more distinction tests with thesestimulus signals, the user input is in sufficiently good agreement withthe really played stimulus signals, a noise signal of only one octavewidth and a noise signal of a width of a second can be used in furtherdistinction tests, and so on, until the user inputs become wrong orunreliable.

It is possible to use static frequency compression, and it is possibleto use dynamic frequency compression. In the latter case, at least oneparameter related to the frequency compression is altered with time, inparticular in dependence of incoming signals.

FIG. 7 is an illustration of a method and an arrangement 1 according tothe invention. The arrangement 1 comprises a computer 1 a with a fittingprogram and a hearing system 10 of which only one hearing device 10 a isillustrated.

The hearing device comprises an output unit 18, e.g., a loudspeaker, anda sound generating unit 13 comprising a noise generator 13 a and a bandpass filter 13 b.

For a fitting session, a hearing device professional 3 and user 2 ofhearing system 10 are present. Hearing device professional 3 operatesthe computer 1 a with the fitting program, through which hearing system10 is controlled at least in so far as stimulus signals are generated byhearing system 10 in the way it is prescribed by said fitting program.Having perceived the two or more stimulus signals of a distinction test,the user will communicate his answer to hearing device professional 3 asindicated by the right-to-left arrow. Hearing device professional 3enters the user input into computer 1 a in which the evaluation andparameter adjustments take place.

FIG. 8 is an illustration of another arrangement 1 according to theinvention. Solid arrows represent audio signals, dotted arrows indicatecontrol signals or data. In this embodiment, user 2 can, fully orsubstantially without external help, carry out a procedure for fitting ahearing device with frequency transposition as sketched above. Allnecessary resources are provided within the hearing system 10 or evenwithin the hearing device 10 a.

Hearing device 10 a comprises an input unit 11, e.g., a microphone, asignal processing unit 12, a sound generating unit 13, a control unit14, a user interface 15 and an output unit 18, e.g., a hearing devicereceiver.

During normal operation of the hearing device 10 a, incoming acousticsound 5 is converted into audio signals, which are processed in signalprocessing unit 12. The processing comprises frequency transposition ofat least a portion of said audio signals, which is dependent on at leastone parameter, which can be controlled or set by control unit 14.Control unit 14 furthermore controls sound generating unit 13, so thatstimulus signals are generated as needed for carrying out distinctiontests, and receives input from user interface 15. Control unit 14ensures that distinction tests are carried out and evaluated properly,and it may, e.g., instruct sound generating unit 13 to generate commandsand messages to be played to the user 2 so as to instruct user duringthe fitting procedure.

LIST OF REFERENCE SYMBOLS

-   1 arrangement, arrangement for fitting a hearing system with    frequency transposition to the hearing preferences of the hearing    system user-   1 a computer with fitting program-   2 hearing system user-   3 hearing device professional, audiologist, fitter-   5 incoming signals, incoming sound-   6 signals to be perceived by the user, outgoing sound-   10 hearing system-   10 a hearing device-   11 input unit, microphone arrangement, acoustic-to-electrical    converter-   12 signal processing unit-   13 sound generating unit-   13 a noise generator-   13 b band-pass filter-   14 control unit-   15 user interface-   18 output unit, loudspeaker, receiver, electrical-to-mechanical    converter-   100-600 steps-   A,A′,A″, B,B′,B″ stimulus signals

1. A method for adjusting a hearing system to the hearing preferences ofa user of said hearing system, wherein said hearing system is capable ofcarrying out frequency transposition of audio signals, which frequencytransposition depends on at least one parameter, said method comprisingA) carrying out a distinction test for examining said user's ability todistinguish between two stimulus signals which differ in their frequencycontents; and B) adjusting said at least one parameter in dependence ofthe result of said distinction test.
 2. The method according to claim 1,wherein said distinction test is related to a test frequency, andwherein said two stimulus signals are chosen such that the sum of theiraudio frequency spectra is substantially symmetrical with respect tosaid test frequency.
 3. The method according to claim 1 or claim 2,wherein said distinction test relates to a test frequency, and whereineach of said two stimulus signals has an audio frequency spectrum, whichis substantially symmetrical with respect to said test frequency and/orwherein the audio frequency spectrum of one of said two stimulus signalsis substantially symmetrical with respect to the audio frequencyspectrum of the other of said two stimulus signals, with said testfrequency forming substantially the corresponding symmetry axis.
 4. Themethod according to claim 1 wherein said two stimulus signals aresubstantially one of noises having different band widths; narrow-bandsignals of different frequencies; narrow-band signals warbling withdifferent warbling amplitudes around substantially the same middlefrequency.
 5. The method according to claim 1, wherein carrying out saiddistinction test comprises a2) consecutively playing said two stimulussignals to said user; b2) receiving from said user informationindicative of whether said user perceived said two stimulus signals astwo times the same sound or as two different sounds; c2) deriving avalue from said information received from said user; wherein said resultof said distinction test is dependent on said value.
 6. The methodaccording to claim 1, wherein carrying out said distinction testcomprises a3) consecutively playing three stimulus signals to said user,wherein these three are chosen from said two stimulus signals eitherfreely or such that one of said two stimulus signals is played exactlyonce; b3) receiving from said user information indicative of which ofsaid consecutively played three stimulus signals was perceived asdifferent from the other two, or indicative of which of saidconsecutively played three stimulus signals was perceived as differentfrom the other two or whether all three consecutively played threestimulus signals were perceived as three times the same sound; c3)deriving a value from said information received from said user; whereinsaid result of said distinction test is dependent on said value.
 7. Themethod according to claim 1, comprising, before step A) the step of G)determining a gain model suitable for said user and using said gainmodel during step A).
 8. The method according to claim 1, comprising,before step A) the step of L) adjusting said two stimulus signals tosubstantially the same loudness.
 9. The method according to claim 1,wherein the frequency contents of said two stimulus signals is relatedto a test frequency, said method comprising the steps of carrying outstep A) at least twice for the same test frequency; adjusting said atleast one parameter in dependence of the results of said distinctiontests.
 10. The method according to claim 1, wherein the frequencycontents of said two stimulus signals is related to a test frequency,said method comprising the steps of carrying out step A) at least oncefor each of at least two different test frequencies; adjusting said atleast one parameter in dependence of the results of said distinctiontests.
 11. The method according to claim 1, comprising carrying out stepA) a multitude of times, each time comprising the steps of x) choosingat least a first and a second stimulus signals from said two stimulussignals; a) playing the chosen stimulus signals to said user; b)receiving from said user information in reaction to step a); c) derivinga value from said information received from said user; wherein saidresult of said distinction test is dependent on said value, and whereinsaid information received from said user is indicative of whether or notsaid user perceived one of said chosen stimulus signals as differentfrom at least one other of said chosen stimulus signals and/orindicative of which one of said chosen stimulus signals has beenperceived by said user as different from at least one other of saidchosen stimulus signals.
 12. The method according to claim 11, whereinsaid value derived in step c) is indicative of the agreement ordisagreement, respectively, between said information received from saiduser and the relation between said chosen stimulus signals.
 13. Themethod according to claim 12, comprising the step of D) statisticallyevaluating said values derived in step c) for said multitude of times ofcarrying out step A), wherein said adjusting said at least one parameteris dependent on the result of said statistical evaluation.
 14. Themethod according to claim 1, comprising the step of repeating step A)after step B).
 15. Use of a distinction test in which the ability of ahearing system user (2) to distinguish between two stimulus signals(A,B; A′,B′; A″,B″) which differ in their frequency contents isinvestigated, for adjusting at least one parameter of said hearingsystem (10), which is capable of carrying out frequency transposition ofaudio signals, and wherein said frequency transposition depends on saidat least one parameter.
 16. Arrangement comprising a hearing system,comprising a signal processing unit comprised in said hearing system,for carrying out frequency transposition of audio signals, whichfrequency transposition depends on at least one parameter; a soundgenerating unit for generating stimulus signals; a user interface forreceiving user input; a control unit operationally connected to saidsignal processing unit, said sound generating unit and said userinterface, and adapted to carrying out a distinction test for examiningthe ability of a user of said hearing system to distinguish between twostimulus signals which differ in their frequency contents; wherein saidcontrol unit is furthermore adapted to adjusting said at least oneparameter in dependence of the result of said distinction test.
 17. Thearrangement of claim 16, which is said hearing system.
 18. A distinctiontest method, comprising the steps of A) investigating the ability of ahearing system user to distinguish between two stimulus signals whichdiffer in their frequency contents; and B) adjusting at least oneparameter of said hearing system; wherein said hearing system is capableof carrying out frequency transposition of audio signals, and saidfrequency transposition is dependent on said at least one parameter.